The utilization of cellulosic waste materials, such as cornstalks, sawdusts, straws, bagasse, and the like, has been the subject of strong interest recently, particularly with respect to utilization of such waste materials for developing alternate sources of fuels, chemicals and other useful products.
It is known that cellulosic materials include three principal components--cellulose, hemicellulose, and lignin. Methods for extraction of hemicellulose have heretofore been suggested and/or utilized and such extracted hemicellulose can be utilized for many existing methods involving hydrolysis, fermentation, pyrolysis and the like.
Lignin has likewise heretofore been isolated from cellulosic materials. Lignin has been found to be higher in hydrogen and carbon and lower in oxygen content than cellulose and hemicellulose and has the highest heating value of the three. Isolated lignin can be burnt directly to generate steam and electricity and can also be used to produce a number of useful products including vanillin, dimethylsulfoxide, dimethyl sulfide, methyl mercaptan, and catechol.
Recovery of cellulose and/or utilization of the same as by acid or enzyme hydrolysis to provide glucose has presented a problem, however, primarily due to the highly ordered crystalline structure of the cellulose molecules and to the presence therein of a lignin seal. Thus, when employing prior art acid hydrolysis processes, it has been necessary to use rather rigorious conditions such that unacceptably low yields of glucose are obtained along with correspondingly large amounts of glucose decomposition products. This generally undesirable result can be appreciated more fully when considering acid hydrolysis as involving the following sequential reaction: ##EQU1## where A is cellulose, B is glucose, and C is undesirable side products. Reports on the acid hydrolysis of woods, based on research conducted during World War II by J. F. Saeman of the U.S. Forrest Products Laboratory, states that the rate of ##EQU2## is about the same as ##EQU3## In other words the formation of side products from glucose occurred at about the same rate as formation of glucose from cellulose. Consequently, the maximum glucose level in the hydrolysate was only 20-30% of the glucose potentially available from the cellulose. Over the years some improvements in yields have been obtained by reducing reaction times, increasing temperature and pressure, and modifying processing equipment. Yet with all these improvements, the best yields obtained to date, using this "conventional" technology, are less than 60%.
Prior art processes which employ enzyme hydrolysis, have resulted in significantly higher yields of glucose with almost no by-product formation. However, because the enzymes can not themselves break or degrade the lignin seal, it is necessary to macerate or grind the raw cellulosic material to a very considerable degree to make enzyme hydrolysis more effective. Obviously, such grinding requires significant amounts of energy which adds to the cost and reduces the attractiveness of enzyme hydrolysis processes.